From DE 103 48 960 A1 a transmission unit is known for the distribution of a drive torque to at least two drive output shafts with at least two, at least three-shaft planetary gearsets. One respective shaft of one gearset is connected to a drive input shaft. Furthermore, one respective shaft of each planetary gearset is one of the drive output shafts, and in each case at least one other shaft of a planetary gearset is in active connection with a shaft of another planetary gearset. An operating-condition-dependent torque in one shaft can be supported as a function of an operating condition of the respective other shaft actively connected thereto via the active connection, in such manner that if there is a rotation speed difference between the drive output shafts, a torque that changes the speed difference is applied via the active connection to the planetary gearsets.
The known transmission unit makes it possible to distribute a drive torque from a drive engine in a drive train of a vehicle, according to need and in relation to the operating situation, in the longitudinal direction of the vehicle between two vehicle axles with a variable degree of distribution or in the transverse direction of the vehicle between the wheels of an axle of a vehicle with a variable degree of distribution.
The use of the transmission unit in an all-wheel-drive vehicle for the variable distribution of a torque in the vehicle's longitudinal direction between two vehicle axles of the vehicle requires, in each case in the area of the vehicle axles, devices by means of which the torque respectively delivered to each vehicle axle can be distributed in the vehicle's transverse direction between the two wheels on a vehicle axle.
Particularly when the transmission device is used in a front-transverse-drive all-wheel vehicle, in which it is desired that the distribution of the drive torque from the engine should be freely adjustable between the front and rear axles of the vehicle, because of the arrangement of the transmission unit as an overlap transmission and that of an axle differential for distributing that part of the drive torque delivered to the front axle of the vehicle in the vehicle's transverse direction between the wheels of the transverse vehicle axle, more structural space is needed in an area of the vehicle in which the drive engine, a gearshift transmission and the front axle of the vehicle are already accommodated.
Of course, the same problem also arises in an all-wheel-drive vehicle in which the drive engine, together with a gearshift transmission, are arranged in the area of the vehicle's rear axle.
Accordingly, the purpose of the invention is to provide a transmission unit which is characterized by taking up less structural space compared with transmission units known from the prior art.